PATCH: enable stacked end_io hooks in buffer.c

[Stefan.Bader@de.ibm.com]

Hi,


I'd like to hook into the end_io reporting chain by replacing the b_end_io
function pointer by an own end_io
function that restores the original values and calls the previous end_io
function after io.
Unfortunatly if the previous function was end_buffer_io_async it unlocks
the bh->b_page too early since
it checks for the b_end_io == end_buffer_io_async.
With the following patch that works but it maybe isn't the best way to do
it. Comments are highly welcome...

Stefan

------------------------
diff -ruN old/fs/buffer.c new/fs/buffer.c
--- old/fs/buffer.c     Thu Jun  7 14:25:57 2001
+++ new/fs/buffer.c     Thu Jun  7 14:31:00 2001
@@ -807,7 +807,7 @@
        atomic_dec(&bh->b_count);
        tmp = bh->b_this_page;
        while (tmp != bh) {
-               if (tmp->b_end_io == end_buffer_io_async &&
buffer_locked(tmp))
+               if (test_bit(BH_Async, &tmp->b_state) &&
buffer_locked(tmp))
                        goto still_busy;
                tmp = tmp->b_this_page;
        }
@@ -839,6 +839,7 @@

 void set_buffer_async_io(struct buffer_head *bh) {
     bh->b_end_io = end_buffer_io_async ;
+               set_bit(BH_Async, &bh->b_state);
 }

 /*
@@ -1531,6 +1532,7 @@
        do {
                lock_buffer(bh);
                bh->b_end_io = end_buffer_io_async;
+               set_bit(BH_Async, &bh->b_state);
                atomic_inc(&bh->b_count);
                set_bit(BH_Uptodate, &bh->b_state);
                clear_bit(BH_Dirty, &bh->b_state);
@@ -1732,6 +1734,7 @@
                struct buffer_head * bh = arr[i];
                lock_buffer(bh);
                bh->b_end_io = end_buffer_io_async;
+               set_bit(BH_Async, &bh->b_state);
                atomic_inc(&bh->b_count);
        }

@@ -2178,6 +2181,7 @@
                bh->b_blocknr = *(b++);
                set_bit(BH_Mapped, &bh->b_state);
                bh->b_end_io = end_buffer_io_async;
+               set_bit(BH_Async, &bh->b_state);
                atomic_inc(&bh->b_count);
                bh = bh->b_this_page;
        } while (bh != head);
diff -ruN old/include/linux/fs.h new/include/linux/fs.h
--- old/include/linux/fs.h      Thu Jun  7 14:26:09 2001
+++ new/include/linux/fs.h      Thu Jun  7 14:25:28 2001
@@ -207,6 +207,7 @@
 #define BH_Mapped      4       /* 1 if the buffer has a disk mapping */
 #define BH_New         5       /* 1 if the buffer is new and not yet
written out */
 #define BH_Protected   6       /* 1 if the buffer is protected */
+#define BH_Async 7 /* 1 if the buffer is used for asyncronous io */

 /*
  * Try to keep the most commonly used fields in single cache lines (16
-----------------

IBM Development, Boeblingen, Germany
Linux for eServer development
Stefan.Bader@de.ibm.com
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